Long polyene and polydiacetylene oligomers: Pariser–Parr–Pople investigation of the geometric and electronic structures in the first 1B u excited state

Abstract

We present Pariser–Parr–Pople (PPP) calculations on long polyene and polydiacetylene oligomers containing up to 32 carbon atoms. Working at both PPP restricted Hartree–Fock and PPP configuration interaction with single excitations levels, we study the excitation towards the 1 1B+u state. We report, as a function of chain length, the evolution of the transition energies and the modifications in geometry and atomic charges along the backbones. Comparison is made between the two series of oligomers. In the longer molecules, localization of the excitation is found, in agreement with the excitonic character of the transition to the 1 1B+u state.